Boron nitride (BN) compounds are in some ways analogous to the carbon system. Boron nitride forms hexagonal and cubic allotropes which are isoelectronic with those of carbon, and a number of properties of BN are similar to those of graphite or diamond. Boron nitride is a useful material in all its forms. Hexagonal boron nitride and amorphous boron nitride are thermal and electrical insulators, and are largely transparent at infrared and microwave wavelengths, as well as being very chemically resistant. Some forms of amorphous boron nitride are also very hard and could serve as wear-resistant and corrosion-resistant coatings.
The properties of cubic boron nitride (cBN) are exceptional. After diamond, cBN is the hardest material known, and since it is more chemically inert than diamond, it is the premier cutting material for ferrous materials. Cubic boron nitride, after diamond, has the highest thermal conductivity of any material. Further, cubic boron nitride has a large band gap and can be doped both p-type and n-type (unlike diamond), and thus cubic boron nitride has great promise as a semiconductor material.
Most low pressure techniques for producing cubic boron nitride also form hexagonal boron nitride and amorphous boron nitride and it is desirable to remove the hexagonal and amorphous forms. However, boron nitride is not easily etched by most acids or bases, although strong mixtures of nitric and phosphoric acids can etch boron nitride slowly at high temperatures.
The present invention overcomes many of the disadvantages of the prior art.